Stage platform control system

ABSTRACT

A system for controlling the positioning of segmented portions of a theater stage or the like. The stage, including the orchestra pit, is divided into segments, each of which has an independent lift apparatus. The respective lift apparatus are controlled from a console which has the capability of providing control of each lift apparatus individually or, alternatively, interconnecting the drive portions of selected lift apparatus together to a common control module for movement of the corresponding stage segments as a unit.

United States Patent 1191 [111 3,812,631

Cruse May 28, 1974 [54] STAGE PLATFORM CONTROL SYSTEM 3,469,354 9/1969 Meetze 52/64 [75] Inventor: William Marion Cruse, Los Angeles,

Calif. Primary Examiner-John E. Murtagh Attorney, Agent, or Firm-Henry M. Bissell [73] Ass1gnee: Henry M. Bissell, Los Angeles,

Calif. a part interest [57] ABSTRACT [22] F1led: Sept. 19, 1972 A system for controllmg the posmonmg of segmented PP 2901337 portions of a theater stage or the like. The stage, in-

' cluding the orchestra pit, is divided into segments,

52 us. 01 52/1, 52/7, 52/64 ehCh 0f which has independent apparatus- The 51 Int. Cl E04h 3/26 respective apparatus are cohtmlled a whole 58 Field at Search 52/64, 126, 7, 6, 10, 1 which has the caPhhihtY Providing each lift apparatus individually or, alternatively, intercon- [56] References Cited meeting the drive portions of selected lift apparatus to- UNITED STATES PATENTS gether to a common control module for movement of the corresponding stage segments as a unit.

3,263,380 8/1966 Bourbonnais 52/7 Rife 52/182 17 Claims, 8 Drawing Figures STAGE PLATFORM CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to theater stage control systems, and more particularly to such systems utilized for the purpose of raising or lowering a theater stage.

2. Description of the prior art It has long been common in the construction of legitimate theaters to provide a system for raising or lowering the stage or particular portions thereof. For purposes of discussion herein, it will be understood that the orchestra pit platform is included in the stage as a portion which is customarily made capable of being raised or lowered. Most such systems utilize hydraulic power as the medium by which the desired force is developed and transmitted to the operative members of the stage lift apparatus. For more than a century the famous Drury Lane Theater in London has used water from the nearby Thames Estuary in a stage lift mechanism. In more recent times other types of systems such as electric motor and cable systems, rack and pinion systems, and the like have been employed, but the majority of the theater stage lift systems rely on hydraulic power. In general these utilize apparatus not unlike the hydraulic lift systems in an automobile service station, except that huge pistons and cylinders are required to handle the much greater loads which are involved. Such systems also require huge reservoirs and accumulators for the great amount of hydraulic fluid which is needed. Moreover pumps and motors of considerable capacity are required in order to handle the loads which are required.

A substantial reduction in the capacity of individual pumps and motors may be realized if the load applied to any one unit is reduced. This can be brought about if the stage is divided into segments, each with an individual lift mechanism. However, the problem then becomes one of providing suitable control of the lift mechanisms for the various segments so that, when desired, the respective portions of the stage may be driven together in unison. The problems inherent in such an approach have heretofore prevented the adoption of a segmented stage and related drive system to the extent and degree of sophistication provided by the present invention.

It is therefore a general object of the present invention to provide an improved stage lift system for theaters and the like.

It is also an object of the present invention to provide a stage lift system for a segmented platfonn.

It is a further object of the present invention to provide a segmented stage lift system including controls for operating the separate segments individually or in unison as selected by an operator.

SUMMARY OF THE INVENTION In brief, particular arrangements in accordance with the present invention include a segmented stage with each separate segment (axis) having its own individual drive system for lifting and lowering. An axis control unit is individually provided for each separate drive mechanism. Each axis control unit has circuitry for preselecting a plurality of positions to which the associated stage segment may be directed when the corresponding drive mechanism is activated. Provision is made for varying the speed of elevating or lowering within a given range as selected by an operator, and with prede termined levels of acceleration and deceleration at the beginning and end of the stage segment movement to provide smooth operation throughout the range of movement.

In addition, a plurality of master control units are provided to which the individual axis control units may be selectively coupled in order to provide control of the individual drive mechanisms in unison by a single operator at a given master control unit. In accordance with an aspect of the invention, the master control units provide for control of movement through preselected incremental distances, thus permitting two or more separate stage segments having a given initial juxtaposition to be moved through the same incremental distance at the same velocity so that the initial juxtaposition is maintained throughout the movement. In addition to providing various control elements for selective adjustment by an operator, the various control units also provide readouts in the form of indications of velocity, position and incremental distance which result from the operation of the associated drive mechanisms.

There are a number of types of actuators or hydraulic motors which may be employed, either directly or in conjunction with cables, shafts, and other force/motion systems to realize the advantages of the present invention. In one preferred embodiment thereof, a positivedisplacement, vane-type rotary hydraulic actuator is utilized in conjunction with a device known as a Rollnut mounted to drive a long jack screw upon which an individual platform segment is mounted. For larger platform segments or where greater loads are involved, two or more such jack screws may be mounted to be driven together to support an individual platform segment. The jack screws may be driven in tandem from a single associated hydraulic actuator or, where heavier loads are involved, separate hydraulic actuators may be used for separate jack screws with the hydraulic actuators being operated from a common axis control unit.

The jack screws are mounted in wells which are deep enough to accommodate the jack screws when they are retracted to the maximum extent. The Rollnut is preferably mounted at the well opening in a fixture which drives the Rollnut in rotation about its longitudinal axis but constrains it against motion along such axis. As a result, the associated jack screw is driven up or down along such longitudinal axis by the rotation of the associated Rollnut. Suitable hydraulic brakes are provided to lock the mechanism when it is located at a desired position.

In one particular arrangement in accordance with the invention, a stage lift control system was provided which utilized 18 separate axis control units capable of being operated independently or together and three master control units which allow collective, synchronized movement of any number and combination of the 18 axis. units. Separate operator control panels were provided for each axis control unit and master control unitutilizing panel displays which continuously show the status of each individual axis control unit and master control unit at any given time. Each of the 18 axis control units includes the electronics needed to provide the desired control function and close the servo feedback loops for an associated electro-hydraulic servo drive mechanism coupled to a corresponding Rollnut/- jack screw combination or set. Synchronous collective lift operation was achieved by the use of position command signals rather than velocity command signals in order to prevent drift between axis control units. Load sensors and associated control circuitry are employed to prevent motion by either an individual axis unit or a group of such units if any single axis or combination of axes is overloaded. The respective control panels incorporate duplicate preset selectors so as' to permit setting the next position profile while each axis or master control unit moves to or dwells at the previous position. Electronic travel limits are provided to maintain closed-loop servo control at the top and bottom of lift travel. However, backup travel limit switches of a mechanical type are provided to remove hydraulic power and set the hydraulic brakes if a given axis servo drive system malfunctions. Automatic velocity limiting is provided to prevent hydraulic supply pressure from dropping below a prescribed minimum value due to excessive fluid flow demands. Also, electronic acceleration limits are provided on all axis control units to limit maximum acceleration for any load up to the maximum and for either direction of travel. In addition to providing preset control of velocity of the selected lift systems, each master control unit also provides a joy stick and associated selector to permit manual control of velocity.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the present invention may be had from a consideration of the following detailed description, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a view, partially cut away, of a segmented theater stage incorporating a stage lift system in accordance with the invention;

FIG. 2 is a diagram of a display and control panel for an individual axis control unit employed in arrangements in accordance with the invention;

FIG. 3 is a diagram of a display and control panel for a master control unit included in arrangement in accordance with the invention; 7

FIG. 4 is a block diagram representing a particular master control unit employed in arrangements in accordance with the invention;

FIGS. 5A and 5B constitute a block diagram representing a particular axis control unit employed in arrangements in accordance with the invention, including both the electronics and the electromechanical servodrive thereof;

FIG. 6 is a block diagram of one particular arrangement in accordance with the invention; and

FIG. 7 is a diagram of a particular manual control device utilized in conjunction with the control units of FIGS. 4 and 5A-5B.

DESCRIPTION OF THE PREFERRED EMBODIMENT Systems in accordance with the present invention, as in the preferred embodiment, utilize a type of linear drive mechanism known as a Rollnut which is driven by a hydraulic actuator. These devices per se form no part of the present invention. The' Rollnut is available from Norco, Inc., of Georgetown, Conn. and is described in detail in the September, 1969 issue of Product Engineering (McGraw-Hill, Inc). under the title New Linear Actuator for High Speeds, Heavy Loads. In essence, the device has the capability of converting rotary motion to linear motion and is utilized in systems in accordance with the present invention to develop up-and-down motion of a screw jack by driving an associted'cylindrical housing in a rotational mode. In a general application the device also has the capability of developing linear motion of the housing by maintaining it stationary against rotation while the associated screw shaft is rotated. Particular advantages provided by the Rollnut are that it has a high conversion efficiency coupledwith a low'starting friction, thus permitting actuation of heavy loads from a small power source,- and it permits accurate positioning of precise devices with very little wear and almost no backlash. Further information concerning design considerations, installation procedures and operating parameters may be found in specification bulletins of Norco, lnc., designated Form Various types of rotary actuators suitable for use as the driving mechanisms in accordance with the present invention are described in an article entitled Rotary Actuators by Ralph Laughman, appearing in Machine Design for September 19, 1968, beginning at page 3 2 A preferred unit for this purpose is obtainable from Moog, Inc., East Aurora, New York, and is described in the Moog C V talo -N9 4Q Referring now to FIG. 1, there is shown a system 10 in accordance with the present invention comprisinga segmented theater stage 12 having various segments 13 and 14 individually supported by associated screw jacks 16. Each screw jack 16 extends from the segment 13 or 14 to which it is attached at its upper end downward into a well or vertical recess (not shown) in the base floor l8 and is supported by an associated gear drive 20 incorporating the Rollnut driving mechanism. The gear drives 20 are in turn coupled by means of drive shafts '22 to associated hydraulic motors (rotary actuators 24). A control console 26 is also shown which incorporates the various displays and control elements for operating the system 10. The complete hydraulic system utilized in the present invention also incorporates other elements (not shown) such as pumps,

reservoirs, valves and the like. In fact, the stage lift system of the present invention is designed to work off a common hydraulic system which may be shared by subsystems for control of theater sets, scenery and the like.

In use, the system 10 may be controlled by an operator at the console 26 to raise or lower various segments l3, 14 of the stage 12 at different selected velocities,

to assume different preselected positions, and to move through preselected incremental distances while maintaining a pre-established staggered juxtaposition relative to one another, allwith due regard for safety considerations against failure or malfunction in order to provide desired theater stage effects demanded by modern stage directing techniques.

As shown in FIG. 1, the segmented stage '12 is cut away by a bisecting transverse plane midway between the front and back of the stage. The stage 12 has 18 individual segments, 12 segments 13 and 6 segments 14. The lift mechanism including the screw jack 1.6 for a single segment such as 13 or 14 is referred to as an axis control unit such as is shown in FIG. 2. Thus, the control console 26 includes 18 axis control units 30 as shown in FIG. 2, each of which includes the'various switches, potentiometers and other control elements as well as the readout displays and indicator lights for a given lift axis. In addition, the system is provided with the capability of operation ofa number of the axis control units in tandem under the control of a master control unit 32 as shown in FIG. 3. In the system 10 of FIG. 1, a console 26 is provided with three such master control units 32 to which any one or a number of the axis control units 30 may be coupled for ganged operation. Each of the control units 30 and 32 is provided with a dual set of controls in order that the operator may pre-set the next control function while the unit 30 or 32 is controlling its associated portion of the system 10 in accordance with the functions previously set into the unit.

As shown in FIG. 2, a single axis control unit 30 comprises a front panel 34 provided with a handle 36. The front panel 34 mounts various switches, dials, lights, meters, etc. including an internal/master selector switch 38 and a preset switch 40. The switch 38 has positions for selecting control of the particular axis control unit internally or from a selected one of the three master control units 32. The pre-set switch 40 is provided to select between the dual velocity and position settings for the unit 30 and also includes a center off position. Dials 42 and 43 are for setting velocity 1 and velocity 2 limits respectively. These dials 42, 43 control ten-turn potentiometers mounted behind the panel 34. A knob 44 is provided for locking the dials 42, 43 at the selected velocities. Digital indicating knobs 48 and 49 provide means for selecting and indicating the digital position of the axis for positions 1 and 2 respectively as selected by the pre-set switch 40. As the knob 48 for example is turned, the digital indicator 50, mounted in the center thereof, changes so that the operator knows the position to which the axis will move when pre-set switch 40 is placed in the position 1. A vemier knob 46 is provided for making a fine adjustment (i1 inch) of the setting of the position dials 48, 49.

Lights 52 and 53 are for the purpose of indicating when the axis is in motion and the direction of movement (up or down). Indicator lights 54 and 55 are provided to give the operator an indication when the axis is in the position selected by the associated position knob 48 or 49. A velocity display meter 56 is provided to give an indication of the actual velocity of the axis associated with a given axis control unit 30. Switch 58 varies the input to the display meter 56 so that the velocity can be read in feet per minute, in current of the associated control circuitry, or in percent of maximum current, as desired. A position display meter 60 provides a readout by incremental position with the scale graduated in feet. A light 62 is provided to give an indication when the particular axis control unit 30 is activated (hydraulic solenoid valve energized). A light 64 is provided to give an overload alarm indication when the capacity of the unit is exceeded by the load demand as evidenced by a reduction in system hydraulic pressure. An overload reset button 66 is provided to reset the circuitry triggered by the overload alarm circuit (FIGS. 5A5B) energizing the light 64.

In FIG. 3, the master control unit 32 has a front panel 70 provided with a handle 72. A pre-set switch 74 is provided for selecting between the two sets of function controls, one being operative to control the master control unit circuitry at a particular time while the other group is set by the operator to become operative at some later time when the pre-set switch 74 is moved to the other position. The sets of function controls comprise direction switches 76 and 77, velocity limit dials 78 and 79, and incremental distance selectors 80 and 81. A locking knob 82 is provided for the dials 78, 79, which are associated with Ill-turn potentiometers mounted behind the front panel 70. A switch 84 permits the master control unit to hold all associated axis drives in a fixed position or to permit them to move under the control setting pre-established by the operator. A velocity display meter 85 provides a reading of velocity of the axis controlled by the unit 32 and an incremental position display meter 86 provides a readout of the movement of the associated axes in feet. As with the axis control unit 30 of FIG. 2, master control unit 32 is provided with an overload alarm light 88 to signal the operator upon the occurrence of an overload in any of the axis control units. However, such an overload will have triggered the overload alarm light 64 in the affected axis control unit 30 so that the overload reset button of that particular control unit 30 is used to reactivate the affected circuit. Position lights 90 and 91 signal the traversal of the controlled axes of the preselected incremental distance. Up and down lights 92 and 93 indicate direction of movement during travel of the controlled axes.

FIG. 4 is a block diagram illustrating the circuitry associated with the master control unit such as 32 shown in FIG. 3. For convenience of identification, the functional blocks represented in FIG. 4 are, to the extent possible, numbered with the same numbers shown in FIG. 3 except that the number is added. Thus, beginning on the left-hand side of FIG. 4, there is shown a pair of incremental distance stages and 181 connected to :E through respective switches 176 and 177, which stages are selectable by means of the A armature of a pre-set switch 174 having three different sections ganged together. Position lights and 191 are provided to be selectively energized by the B armature of switch 174. A move/hold switch 184 is connected to control a null detector stage 202 which serves to energize the position lights 190, 191. Velocity limit stages 178, 179 are selected by the C armature of switch 174, the signal from which is applied to a deceleration filter 204 and then to a clamp stage 206. A reference voltage E is commonly applied to the velocity limit stages 178, 179 through a switch 208 which, in its other position, substitutes a voltage E, which is derived from the joy stick arrangement of FIG. 7 and which will be described in further detail hereinbelow.

The master control unit 32 of FIG. 4 also includes a master velocity display meter 185, an incremental position display meter 186, and an overload alarm stage 188. Direction indicator lights 192 and 193 are connected through diodes 210 to the output of the incremental distance signal amplifier 212 adjacent the null detector 202. An acceleration stage 214 has its input connected to +E potential and provides an output signal to an integrating amplifier 216 which is connected with a clamp stage 206 in its feedback loop. The output of the incremental distance amplifier 212 is applied to a velocity clamp 218 which supplies an input signal to another amplifier stage 220 coupled to drive a DC instrument motor 222 which in turn, through an instrument gear stage 224, drives a ten-tum potentiometer 226. Feedback control of the amplifier 220 and motor 222 is provided by means of a tachometer 228 connected in the feedback loop. The motor power supply 230 is coupled to the motor 222 and connected to the null detector 202 which provides a reset/operate signal to the power supply 230, the integrating amplifier 216 and the deceleration filter 204. An overall servo feedback loop is provided from the IO-turn potentiometer 226 via a buffer amplifier 232 to the negative input of the incremental distance amplifier 212 and also to the master control unit selector switch in the 18 associated axis control units. (FIG. A).

FIGS. 5A and 5B represent in block diagram form the circuitry associated with the axis control unit 30 of FIG. 2. Pre-set position stages 148 and 149 are connected to receive an input from $13 potential and provide an output via the A armature or pre-set switch 140 to an amplifier 304. Associated vernier position stages 301 and 302 provide another signal to the amplifier 304 via the B armature of the preset switch 140. The stages 301, 302 receive inputs +E or Evia the vernier switch 146 and thus provide an adjustment of :1 inch for the position setting of the corresponding position switch 148 or 149. Velocity limit stages 142 and 143 provide a signal to a deceleration filter 306 via the C armature of the pre-set switch 140 and receive inputs from the potential E or E, via a switch 308.

The remaining input to the amplifier 304 is received via a selector switch 138 from a selected one of the three master control units (FIG. 4) or, in the event that internal control is utilized, this signal line is switched to an open position. The output of the amplifier 304 is applied via a position travel limit stage 310 to an amplifier 312. A maximum velocity limit stage 314 is coupled via a B section of the selector switch 138 to provide an input to a velocity clamp 316 when the axis control unit is connected to one of the master control units. The velocity clamp 316 receives a further control from the minimum clamp level stage 318 and processes the output of the amplifier 312 in accordance with these limit potentials. The output of the velocity clamp 316 is applied through an overload hold stage 320 (FIG. 58) to the positive input of an integrating amplifier 22, thence to a servo amplifier 324 which controls a servo valve 326 in the hydraulic line. A pressure switch (section C of the selector switch 138) is coupled to apply a signal to the overload hold stage 320 and an overload alarm 164. Overload reset stage 166 is provided to apply a resetting signal to the hold stage 320 which is controlled by an amplifier 342 which compares the drive signal to the servo amplifier 324 with a potential provided by an overload set point stage 340 (internal adjustment). A null detector 330 (FIG. 5A) receives inputs from amplifier 312 and overload hold stage 320, and applies a reset/operating signal to a line leading to the deceleration filter 306, an integrating amplifier 332 and a minimum amplifier limit stage 334. The integrating amplifier 332 receives its positive input from the acceleration limit stage 336 and receives its negative input from the deceleration filter 306 via a clamp 338. A ramp voltage signal from the amplifier 332 is applied through switch 138 B to velocity clamp 316 to control the limits of acceleration. The output of the minimum amplifier limit stage 334 is applied as a reset/operating'signal to the integrating amplifier 322.

Mechanical limit switches provide a +E potential (as shown in FIG. 6) via a switch 334 to the solenoid valve 346 in the hydraulic fluid line. The switch 344 is mounted on the joy-stick control device of FIG. 7 and in effect activates or dcactivates the hydraulic portion of the axis control unit 30. From the solenoid valve 346, pressurized fluid is applied to the servo valve 326 and to a hydraulic brake stage 350. The servo valve 326 applies pressure over one line or another to a counterbalance valve 352 which in turn drives the hydraulic motor 354 and is provided with cross-port relief'valves 356. Both the hydraulic motor 354 and the hydraulic brake 350 are coupled to a power gearing stage 360 which drives the Rollnut 362 that in turn drives the screw jacks to raise or lower the assocated stage segment. Tachometer feedback is provided from the hydraulic motor 354 via a tachometer 370 to the negative input of the integrating amplifier 322. The velocity/current meter display 156 is connected to' the feedback line of the tachometer 370 for velocity indication or to the output of the integrating amplifier 322 for a current reading via switch 158. A further feedback loop is provided from the hydraulic motor 354 to the negative input of the amplifier 312 via instrument gearing stage 374, a slip clutch 376, a precision potentiometer 378 and a buffer amplifier 380. The position meter display 160 is coupled to this loop at the output of the buffer amplifier 380.

Referring now to FIG. 6, there is shown in block diagram form a representation of the way in which the master control units of FIGS. 3'and 4 are interconnected with the axis control units of FIGS. 2 and 5A-5B, together with the related hydraulic system and common control stages to provide the desired operation of the system 10. In FIG. 6, master control units 32 (numbers 1, 2 and 3) are interconnected with axis control units 30 (indicated from number 1 to number 18) and their associated drive mechanisms (indicated by reference numerals 30A). Lines from the left-hand side of each of the master control units 32 (the negative input to the amplifier 212 of FIG. 4) are applied in common to respective points on the A section of switch 138 in each axis control unit. Similarly, lines from the right-hand side of master control units 32 (the righthand input to the null detector 202) are applied in common to the C sections of switch 138 in each of the axis control units 30. The mechanical limit signal is provided by an upper limit switch 400 and a lower limit switch402 from +E potential to the solenoid valve 346 via a microswitch 344 (see FIG. 5B) of each axis control unit 30. Hydraulic fluid under pressure is supplied from a hydraulic source 404 to each of the axis control units 30. The potential E ,a velocity command reference voltage-is developed from an amplifier 410 as the comparison of a velocity reference V); with the output of another amplifier 412 which in turn provides a comparison of signals from a minimum pressure set point stage 414 and a transducer 416 which monitors the pressureof the fluid from the hydraulic source 404. The output of the amplifier 412 is also supplied through a level indicator 418 to the overload alarm stage 188 (see FIG. 4) of each of the master control units 32.

In operation of the system 10, the operator first sets up to control a particular axis from the associated axis control unit alone or, together with a number of other axis control units, from one of the three master control units 32. If he is to control a single axis (segment of the stage) he directs his attention to the associated axis control unit 32 and proceeds to set the velocity limit and position controls to levels which he wishes the stage to assume. As the stage segment is moving to the selected position at the selected velocity, he can pre-set the next position and velocity limit in preparation for transferring control to the second set via the pre-set switch 40 (FIG. 2). Should he wish to control a number of axes from a single master control unit 32, he directs his attention to the master control unit and, in similar fashion, adjusts the settings of the velocity limit and incremental distance controls, using the pre-set selector switch 74 (FIG. 3) to establish or pre-set the performance of those axis units which are coupled to the master control unit 32. In this way, either an individual axis or a group of axes has independent or simultaneous control over velocity and direction of movement. Protection is provided by the overload circuitry so that both individual and group motion of the axes is affected if any single axis or combination of axes is overloaded. The hydraulic supply pressure is prevented from dropping below a prescribed minimum value as the result of excessive flow demands by means of the automatic velocity limiting which reduces demand to compensate. The various panel indicators such as 56, 60 of FIG. 2 and 84, 86 of FIG. 3, together with the respective indicator lights, alarms, etc., permit the operator to continuously monitor the state of each axis and group of axes.

A further control feature is demonstrated in FIG. 7 which is a side elevation, partially broken away of a manual (joy stick) control 500. One such joy stick is provided on the control console 26 (FIG. 1) for each of the three master control units 32 and the 18 axis control units 30. The handle 502 of the joy stick unit 500 is moved up or down by the operator in order to develop the desired control. As the handle 502 moves out of the center rest position, the microswitch 344 (see FIG. B) is closed to activate the associated hydraulic lift portion of the system. The joy stick 500 contains a potentiometer 504 which develops a voltage at the armature 506 between +13 and E. This selected voltage is designated E, and may be substituted for the velocity command reference voltage E at the input to the velocity limit stages in the master control unit 32 (see FIG. 4) and the axis control unit 30 (see FIG. 5A). When the joy stick 500 is operative in this fashion, the operator is enabled to manually control the velocity of the associated axis or group of axes as desired by moving the handle 502 (within the limits establisbed by the velocity limit stages).

There have thus been described particular arrangements in accordance with the present invention of a stage platform control system which permits an operator to control various segments of a segmented stage individually or in groups. The operator may pre-set the next performance profile and, upon activating a selector switch, cause the stage sections to move to a predetermined incremental distance with controlled velocity and acceleration. The operator may vary the position of a given segment by as little as one inch through a vernier adjustment. Movement of the stage sections is smooth, quiet, rapid, and precise. The system operates with minimum demands on the hydraulic pressure source and with a minimum of space required for the various lift mechanisms. No large reservoirs for hydraulic fluid are required, since the hydraulic actuator units which are employed together with the Rollnut and 6 screw jack lifting mechanisms eliminate the need for such. Moreover, systems in accordance with the invention, although more sophisticated and effective than prior hydraulic or cable lift systems for theater stages, are generally less expensive than the bigger, more cumbersome and more limited systems presently in use.

If desired, alternative arrangements may be incorporated in stage lift systems in accordance with the invention without departing from the concept thereof. For example, other lift mechanisms may be substituted for the Rollnut and screw jack combination of the preferred embodiment. One such alternative arrangement is a gear box drive utilizing a vertical rack-and-pinion combination with suitable guidance for the vertical movement by bearings such as ball bushings or the like. Other types of hydraulic actuators with associated valving and hydraulic controls may also be substituted for what has been shown and described hereinabove, all within the principle of unit operation and associated control as disclosed. Indeed, should appropriate electric motors and drives be designed, it may be feasible to substitute such electric motor drive combinations for the hydraulic actuators and drives employed herein, although such motors as are presently known neither develop the required capability nor operate with such quietness that they can be tolerated in stage lift systems where the drives are necessarily placed in such close proximity to the audience.

Moreover, although the present invention has been shown and described in the context of a system for vertical position and movement control, it should be understood that the principles disclosed and claimed herein are also applicable to the control of stage segments movable in other coordinates. Thus where the need arises for control of movable stage segments in horizontal or angled attitudes, the present invention may be utilized for such purposes as well. One particular example of such is a recently expressed request for a segmented stage in the form of a circular turntable surrounded by separately movable curved segments with the separate portionsto be rotatable together with synchronized control or separately under individual control as selected. The master/axis control principle of the present invention presents an ideal solution to such a need.

Although there has been described hereinabove one specific arrangement of a stage lift system in accordance with the invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention.

What is claimed is:

1. A stage platform control system for theaters and the like comprising:

a plurality of stage segments capable of separate movement relative to each other;

a plurality of drive mechanisms individually associated with corresponding stage segments to position said segments on command;

a plurality of control means associated with the drive mechanisms for selectively actuating the drive mechanisms, said control means including means for actuating all or less than all of the drive mechanisms concurrently for movement in response to a single set of control signals, said control means including duplicate sets of controls for permitting the preprogramming of one set of controls during the time the other set of controls is in operative use,

and

means for alternatively selecting one of said sets of controls for operative use.

2. Apparatus in accordance with claim 1 wherein said control means comprises a first plurality of axis control units individually associated with corresponding ones of the drive mechanisms and a second plurality of master control units capable of selective association with any or all of the axis control units.

3. Apparatus in accordance with claim 1 wherein the control means include means for limiting the acceleration, velocity, and limit of travel of the drive mechanisms.

4. Apparatus in accordance with claim 1 further including means for automatically controlling associated drive mechanisms in accordance with the condition of the active set of controls.

5. Apparatus in accordance with claim 1 further including means for providing a display indicative of position, velocity, direction of movement, and incremental motion of the drive mechanisms.

6. Apparatus in accordance with claim further including means for providing an indication when a particular drive mechanism associated with a particular control means is in the position corresponding to the setting of the particular control means.

7. Apparatus in accordance with claim 2 wherein each axis control unit includes means connecting said axis control unit to each of the master control units and a switch for selecting one of the master control units for operative association therewith, said switch further including a position for internal operation of the axis control unit.

8. Apparatus in accordance with claim 4 further including means for manually controlling position and velocity of associated drive mechanisms, and means for substituting said manual control means for the automatic velocity controls in the respective control means.

9. Apparatus in accordance with claim 3 wherein the drive mechanisms comprise a plurality of hydraulic actuators individually associated with respective stage segments to develop the force for driving the stage segments, and further including a source of pressurized hydraulic fluid in a system for applying said pressurized hydraulic fluid to said actuators.

10. Apparatus in accordance with claim 9 wherein the applying means comprises means coupled to the control means for controlling the application of pressurized fluid to the actuators in response to electrical control signals from the associated control means.

11. Apparatus in accordance with claim l0-further including a pressure transducer responsive to hydraulic system pressure, and means coupled to the transducer for reducing the drive to the hydraulic actuators in response to a reduction in hydraulic system pressure.

12. Apparatus in accordance with claim 11 further including means coupled to the transducer for providing an alarm indication in the event of a reduction in hydraulic line pressure below a pre-establishedminimum level. i

13. Apparatus inaccordance with claim 11 wherein the means for reducing the actuator drive comprises means for summing signals from the velocity limit stages of the axis control units in active operation and means for comparing the result of said summing operation with a signal from the transducer in order to reduce the actuator drive when the summed signal is less than a predetermined value.

14. Apparatus in accordance with claim 1 wherein the stage segments are movable vertically and the drive mechanisms are operable to move the stage segments up and down in response to signals from the control means.

15. Apparatus in accordance with claim 14 wherein the control means includes means for controlling the drive mechanisms of a plurality of offset stage segments to move said stage segments in unison through the same incremental distance.

16. A stage control system comprising:

a plurality of axes, each including a movable stage segment, an associated drive mechanism, and hydraulic control means for actuating the drive mechanism from a common hydraulic pressure system;

17. A system in accordance with claim 16 further including means for reducing proportionally the drive to all axes upon occurrence of a reduction in hydraulic system pressure. 

1. A stage platform control system for theaters and the like comprising: a plurality of stage segments capable of separate movement relative to each other; a plurality of drive mechanisms individually associated with corresponding stage segments to position said segments on command; a plurality of control means associated with the drive mechanisms for selectively actuating the drive mechanisms, said control means including means for actuating all or less than all of the drive mechanisms concurrently for movement in response to a single set of control signals, said control means including duplicate sets of controls for permitting the Preprogramming of one set of controls during the time the other set of controls is in operative use; and means for alternatively selecting one of said sets of controls for operative use.
 2. Apparatus in accordance with claim 1 wherein said control means comprises a first plurality of axis control units individually associated with corresponding ones of the drive mechanisms and a second plurality of master control units capable of selective association with any or all of the axis control units.
 3. Apparatus in accordance with claim 1 wherein the control means include means for limiting the acceleration, velocity, and limit of travel of the drive mechanisms.
 4. Apparatus in accordance with claim 1 further including means for automatically controlling associated drive mechanisms in accordance with the condition of the active set of controls.
 5. Apparatus in accordance with claim 1 further including means for providing a display indicative of position, velocity, direction of movement, and incremental motion of the drive mechanisms.
 6. Apparatus in accordance with claim 5 further including means for providing an indication when a particular drive mechanism associated with a particular control means is in the position corresponding to the setting of the particular control means.
 7. Apparatus in accordance with claim 2 wherein each axis control unit includes means connecting said axis control unit to each of the master control units and a switch for selecting one of the master control units for operative association therewith, said switch further including a position for internal operation of the axis control unit.
 8. Apparatus in accordance with claim 4 further including means for manually controlling position and velocity of associated drive mechanisms, and means for substituting said manual control means for the automatic velocity controls in the respective control means.
 9. Apparatus in accordance with claim 3 wherein the drive mechanisms comprise a plurality of hydraulic actuators individually associated with respective stage segments to develop the force for driving the stage segments, and further including a source of pressurized hydraulic fluid in a system for applying said pressurized hydraulic fluid to said actuators.
 10. Apparatus in accordance with claim 9 wherein the applying means comprises means coupled to the control means for controlling the application of pressurized fluid to the actuators in response to electrical control signals from the associated control means.
 11. Apparatus in accordance with claim 10 further including a pressure transducer responsive to hydraulic system pressure, and means coupled to the transducer for reducing the drive to the hydraulic actuators in response to a reduction in hydraulic system pressure.
 12. Apparatus in accordance with claim 11 further including means coupled to the transducer for providing an alarm indication in the event of a reduction in hydraulic line pressure below a pre-established minimum level.
 13. Apparatus in accordance with claim 11 wherein the means for reducing the actuator drive comprises means for summing signals from the velocity limit stages of the axis control units in active operation and means for comparing the result of said summing operation with a signal from the transducer in order to reduce the actuator drive when the summed signal is less than a predetermined value.
 14. Apparatus in accordance with claim 1 wherein the stage segments are movable vertically and the drive mechanisms are operable to move the stage segments up and down in response to signals from the control means.
 15. Apparatus in accordance with claim 14 wherein the control means includes means for controlling the drive mechanisms of a plurality of offset stage segments to move said stage segments in unison through the same incremental distance.
 16. A stage control system comprising: a plurality of axes, each including a movable stage segment, an associated driVe mechanism, and hydraulic control means for actuating the drive mechanism from a common hydraulic pressure system; control means for selectively providing control of one or more of said axes; and means for limiting the drive to all axes controlled in common upon occurrence of an overload condition in any one of the axes under common control.
 17. A system in accordance with claim 16 further including means for reducing proportionally the drive to all axes upon occurrence of a reduction in hydraulic system pressure. 